Automatic focusing arrangement

ABSTRACT

A split image of a vertical edge of an object is formed by a standard range finder, the two half images coinciding in a vertical direction when the objective lens is properly focused. An oscillating mirror reflects light along a horizontal line including the top half image onto a first photocell and light along a horizontal line including the bottom half image onto a second photo-cell. The photocells thus emit a scanning signal when the respective half images are reflected thereon. A first and a second threshold circuit is responsive to these scanning signals and the outputs of the first and second threshold circuit are applied each to one input of and AND-gate, the output of which causes the motor positioning the objective lens to stop upon simultaneous receipt of the scanning signals.

United States Patent [191 Wick et al'. 0

AUTOMATIC FOCUSING ARRANGEMENT Inventors: Richard Wick; Alfred Winkler;

Bernhard Von Fischern, all of Mnnich, Germany Agta-GevaertAktiengesellschait, Leverkusen, Germany Filed: Dec. 23, 1971 Appl. Noi:211,373

Assignee:

[30] Foreign Application Priority Data Dec. 24, 1970 Germany ..P 20 63705.2

References Cited UNITED STATES PATENTS 2/1968 Townsley ..9s/44c 3/1971Appleby ..250/209 [111 3,733,989 1 May 22, 1973 2,944,154 7/1960 Bosch..250/209 3,270,647 9/1966 Jakob et al... ..95/44 C 3,623,811 11/1971Lederer ..95/44 C Primary Examiner-Samuel S. Matthews AssistantExaminer-E. M. Bero Attorney-Michael S. Striker [57] ABSTRACT A splitimage of a vertical edge of an object is formed by a standard rangefinder, the two half images coinciding in a vertical direction when theobjective lens is properly focused. An oscillating mirror reflects lightalong a horizontal line including the top half image onto a firstphotocell and light along a horizontal line including the bottom halfimage onto a second photocell. The photocells thus emit a scanningsignal when the respective half images are reflected thereon. A firstand a second threshold circuit is responsive to these scanning signalsand the outputs of the first and second threshold circuit are appliedeach to one input of and AND-gate, the output of which causes the motorpositioning the objective lens to stop upon simultaneous receipt of thescanning 'signals.

13 Claims, 13 Drawing Figures PATENTEI] W 2 21973 SHEET 1 OF 4 I 3 A b--INVENTOR$ gm. DR. RICHARD WICK BY LALFRED WINKLER BERNHARD v. FISCHERNPATENTE W22 m5 SHEET 2 OF 4 Fig.7 [2

BERNHARD v. FISCHERN 1 AUTOMATIC FOCUSING ARRANGEMENT BACKGROUND OF THEINVENTION The present invention relates to a photographic camera, andmore specifically to an automatic focusing arrangement for such camera.Even more particularly it circuit arrangement whose input is derivedfrom a lightsensitive element. Such an electronic circuit may forexample cause the motor moving the lens to be deenergized when the lenshas been moved to the proper position wherein the object to bephotographed is properly focused.

SUMMARY OF THE INVENTION It is an object of the present invention tofurnish an automatic focusing arrangement of the abovedescribed type inwhich the movement of the lens is stopped in a simple and reliablemanner whenever the object to be photographed is in sharp focus on thefilm plane.

The present invention comprise lens means and moving said'lens meansbetween a first and second end position. It further comprises opticalmeans which create a split image of a determined portion of the objectto 'be photographed, said split image comprising a first and second halfimage. The two half images are aligned when the object to bephotographed is in sharp focus and are misaligned, that is displacedfrom one-another in a first direction, when the object is not in sharpfocus. Scanning means scan in said first direction along a first andsecond scanning path which, respectively, include said first and secondhalf images. Said first and second scanning means respectively furnishfirst and second scanning signals when scanning said first and secondhalf image. Finally, control means are interconnected between saidscanning means and said moving means for stopping said moving means uponsubstantially simultaneous receipt of said first and second scanningsignal.

More specifically, a known type of optical system creating a split imageis used in conjunction with a first diaphragm. An oscillating mirrorscans the section of the diaphragm having the first and second halfimage. Light from the first half image is reflected onto a firstphotosensitive element, while light from the second half image isreflected onto a second photosensitive element. The photosensitiveelements are each connected to the input of a control circuit. The firstand second control circuits each comprise pulse-forming stages, theoutput of each of these pulse-forming stages beingapplied to an outputstage which is an AND- circuit. The output from the AND-circuit causes adeenergization of the servomotor moving the lens.

More specifically, when the lens is in a position whereinthe object isnot in proper focus, thefirst and secondhalf image are displacedfromeach otherin a first direction, for example horizontally. The firstdiaphragmhas a first and second horizontal slit, respectivelyencompassing a portion of thefirst and second half image. Theoscillatingmirror reflects consecutive horizontal portions of the first and secondhorizontal slit consecutively upon the first and-secondphotosensitiveelement, respectively. When the scanning mirror reflects the first orsecond half image, a corresponding output from the photosensitiveelement results. The photosensitive elements will thus furnish outputsignals simultaneously only when the two half images are aligned, thatis when the lens is correctly positioned for focusing the objects ontothe film plane. Simultaneous generation of a signal in thephotosensitive element will cause a simultaneous input to the two inputsof the AND-gate mentioned above, thereby causing an output I of saidAND-gate which in turn stops the motor moving the lens.

In a further embodiment of the present invention, the pulse-formingstages associated with each of the lightsensitive elements compriseamplifiers, equalizers, differentiating circuits and rectifiers. In aparticularly embodiment of the present invention the equalizing elementsare Schmitt triggers.

The rectifiers associated with each of the pulseforming stages areconnected to the first and second inputs of the above-mentionedAND-gate, each through an emitter-follower stage.

Each of said emitter-follower stages may, in a preferred embodiment, beconductive in the presence of scanning signals signifying a half imageand nonconductive in the presenceof scanning signals resulting from theabsence of a half image.

The output of the above-mentioned AND-gate may be connected to the gateof a thyristor, whose anodecathode circuit is connected to the base of aswitching transistor. The servomotor moving the lens may then beconnected into the collector-emitter circuit of the switchingtransistor.

The means oscillating the scanning mirror control said mirror in such amanner that the amplitude of oscillation is restricted to the length ofthe slit in the diaphragm.

In a further preferred embodiment of the present invention the lens maybe moved into an end position, for example the position forphotographing a distant object, after the exposure has been made.Specifically, the movement of the objective may be linked to the filmtransport.

Photovoltaic cells may be used as the photosensitive elements in apreferred embodiment of the present invention.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following de scription of-specificembodiments when read in connectionwith the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic diagram of afocusing arrange ment of the present invention;

FIG. la is aperspective diagram showing the. optical split image system;

FIG. 1b is a diagram showing the drive forthe'seanning mirror;

FIG. 2 shows an alternate optical system for generating a split image;and

FIG. 2a shows: the ground glass image for the optical system of FIG. 1;

DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of thepresent invention will now be described with reference to the drawing.

As shown in FIG. 1, the optical system for furnishing a split imagecomprises a lens 1 and 2, a stationary mirror 3, a mirror 4 mounted foroscillation around an axis and driven by a gear 5 which in turn iscoupled to a servomotor 6. The optical system further comprises a splitimage prism 7, a convex lens 8 and a diaphragm 9.

An oscillating mirror 10 is arranged behind the diaphragm 9. Thisoscillating mirror is oscillated by a gear 11 which in turn is driven bya drive system 12 to be described below. A further convex lens hasreference numeral 13, and a second diaphragm is designated by referencenumeral 14.

As shown in FIG. 1a, diaphragm 9 has two horizontal slits 15, 16arranged one on top of the other. Diaphragm 14 has similar slitsnumbered 17 and 18. A photoelement 19 is arranged at the height of slit17, while a photoelement 20 is arranged at the height of slit 18 ofdiaphragm 14.

Referring again to FIG. 1, the photoelement 19 is connected to the inputA1 of a control circuit whose output controls the energization ofservomotor 6. Specifically, terminal Al designates the input of anamplitier 21 whose output is connected to the input of a Schmitt trigger22. The output of Schmitt trigger 22, labelled B1, is connected to adifferentiating circuit comprising a capacitor 23 connected to aresistance 24. The common terminal of capacitor 23 and resistance 24 islabelled C1. The output of the differentiating means, namely the signalat terminal C1, is applied through a rectifier D1 poled to permit thepassage of positive pulses, to the base of a transistor 28. The terminalat the base of transistor 28is labelled E1. It is also the tap of avoltage divider connected from the positive battery side to the negativeor ground side and comprising a resistance series-connected to aresistance 27. Transistor 28 is connected as an emitterfollower and hasan emitter resistance 29. The values of resistors 26 and 27 are sochosen that transistor 28 is cut off in the absence of a signal atterminal D1.

Similarly, photoelement 20 is connected to the input A2 of an amplifier32 whose output is connected to a Schmitt trigger 33. The output of theSchmitt trigger appears at a terminal B3 and is differentiated by acapacitor 34 and a resistance 35. The common point of resistance 35 andcapacitor 34 is labelled C2 and is connected to the anode of a diode 36whose cathode is connected to the base of a transistor 39. Similarly, totransistor 28, transistor 39 is kept at a cut-off condition in theabsence of a signal at terminal D2 by means'of a voltage dividercomprising a resistance 37 seriesconnected to a resistance 38.Specifically, the base of transistor 39 is connected to the voltagedivider tap of this voltage divider, which also constitutes terminal D2.Again, transistor 39 has an emitter resistance 40. The emitter oftransistor 28 is connected to the cathode of a diode 30 whose anode isconnected to a resistance 31. The anode of diode 30 is also connected tothe anode of a diode 41 whose cathode is connected to the emitter oftransistor 39. The free terminal of resistor 31 is connected to thepositive supply line. The anodes of diodes 30 and 41 are connected tothe control gate of a thyristor 42 whose anode is connected to thepositive supply line via a resistance 43 and to the negative sup plyline via a resistance 62. The anode of thyristor 42 is further connectedto the base of a switching transistor 44 into whose emitter-collectorcircuit are connected servomotor 6 and a resistance 63. The overallcircuit is energized by a battery 45 which is connected into the circuitupon closure of a switch 46. Servomotor 6 drives the lens system 47 in adirection indicated by a and b.

FIG. lb shows the mechanism for oscillating mirror 10. Specifically itcomprises an escapement-type mechanism having a latch 110 and gears 108and 109. A cam 106 operates a contact 104 which periodically connects avoltage source 103 to a magnetic coil 101. Coil 101 is part of a relaywhose armature moves back and forth in synchronism with the energizationand deenergization of coil 101, that is in synchronism with the closingof contact 104. When coil 101 is de-energized, a spring 102 returns thearmature to the original position. The motion of the armature is coupledto mirror 10 through gear 1 1 which causes oscillation of said mirror.

An alternate optical system for furnishing a split image is shown inFIG. 2. The optical system shown in FIG. 2 is particularly useful in areflex camera. Reference numeral 50 denotes a ground glass plate havingtwo separate prism halves 51 and 52. 53 denotes a rotatively mountedmirror, while reference numeral 54 denotes the lens which may be movedin direction 0 or direction d. Mechanical coupling 55 connects the lensto servomotor 6. When lens 54 is incorrectly positioned for sharpfocusing of the object, a split image (60,61) results on ground glassplate 50. This is similar to the split image created by an incorrectpositioning of lens 47 and mirror 4 in FIG. 1. The latter resulted inthe split image comprising half images 58 and 59.

If now the drive system 12 is energized either when the shutter iscocked or during operation of the film transport, then gear 11 starts tooscillate mirror 10 in direction e and f. The mirror thus scans slits 15and 16 of the optical system. When the mirror reflects a half image 58or 59, the output of photosensitive elements 19 and 20 changerespectively. FIG. 3a and 3b show, respectively, the output ofphotoelements 19 and 20 during the scanning of slits 15 and 16. FIGS. 4aand 4b show the outputs at the corresponding Schmitt triggers 22 and 33which result from the variation of-photosensitive element outputs shownin FIGS. 3a and 3b, respectively.

The rectangular pulses shown in FIGS. 4a and 4b are differentiated,resulting, respectively, in the signals shown in FIGS. 5a and 5b.

The negative signals are then eliminated by rectifiers D1 and D2respectively, resulting in the signals shown in FIGS. 6a and 6b. Theseare the signals appearing at terminals D1 and D2, respectively.

It will be noted that the pulse at terminal D1 appears prior to thepulse at terminal D2. A positive pulse ap- 'pearing at terminal D1causes transistor 28 to become highly conductive, in turn causing itsemitter to be at substantially the full battery voltage. At this pointdiode 30 blocks, so that this positive pulse cannot be furthertransmitted. At the time at which the positive pulse appears at terminalD1, as stated above, no pulse appears at terminal D2, thus causingtransistor 39 to remain blocked. Thus, the cathode of rectifier 41 isconnected to the negative line via resistance 40. Rectifier 41 is thusconductive and the gate of thyristor 42 is connected to what issubstantially the negative supply potential. Thus, thyristor 42 remainsblocked. Since thyristor 42 is blocked, the base of transistor 44 issubstantially at the potential of the positive supply line, causing ofmirror 4. The first and second half image 58 and 59 thus commence tomove closer to one another. Thus, the time difference between the twopulses shown in FIGS. 6a and 6b decreases.

The pulses at terminals D1 and D2 will of course fin'ally coincide,thereby causing simultaneous blocking of diodes 30 and 41. The gate ofthyristor 42 will then receive a positive voltage via resistance 31,causing thyristor 42 to fire. Firing of thyristor 42 in turn causestransistor 44 to block, thereby de-energizing motor 6 and causing thelens 47 and mirror 4 to stop moving. At this point a sharp image of theobject to be photographed is created in the film plane. The abovedescription of course indicates that diodes 30 and 41 in combinationwith resistance 31 constitute an AND-gate. It should further be notedthat the criterion for stopping the motor is developed strictly from achange in the output of photosensitive elements 19 and 20, whichare in apreferred embodiment of the present invention, photovoltaic cells. Theswing of mirror 10 must thus be controlled to avoid the scanning of theedges of slits l5 and 16 (the vertical edges) since this would give afalse indication of split image coincidence. Slits l7 and 18 must beshort relative to slits and 16, or photovoltaic cells 19 and 20 mustcover a short horizontal distance only, since these cells will of courserespond substantially equally to light falling on any portion thereof.

Operation of the camera release button will then cause opening of switch46 and may also be used to disconnect the drive 12 from mirror 10. It isof course also possible to provide a separate switch or key foroperating switch 46 and, simultaneously therewith energizing drivesystem 12. Release of such a separate key or switch may then causecontact 46 to open and drive system 12 to be disconnected.

It is further possible to disconnect the automatic focusing arrangementincluding mirror oscillating means l2'whenever the lens reaches thesecond end position. This would improve the operation in the unlikelyevent that automatic focusing did not take place.

While the invention has been illustrated and described as embodied inspecific scanning, optical and control systems, it is not intended to belimited to the details shown, since various structural and circuitchanges may be made without departing in any way from the spirit of thepresent invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims:

1. In a photographic camera, an automatic focusing arrangement,comprising, in combination, lens means; moving means moving said lensmeans along a predetermined path between a first and second endposition; optical means creating a split image of a determined portionof an object to be photographed, said split image comprising a first andsecond half image displaced from each other along a first axis when saidlens means is incorrectly positioned for focusing said object andcoinciding when said lens means is correctly positioned for focusingsaid object; oscillating mirror means mounted to reflect said first andsecond half image, respectively, back and forth along a first and secondpredetermined path parallel to said predetermined axis; first and secondphotosensitive means respectively mounted in corresponding positionsalong said first and second predetermined path for receiving saidsoreflected first and second half images respectively and furnishing afirst and second scanning signal, respectively, in response thereto; andAND-gate means having a first and second input respectively connected tosaid first and second photosensitive means and an AND-gate outputconnected to said moving means, for deenergizing said moving means inresponse to simultaneous receiptof said first and second scanningsignals, whereby said moving means are stopped upon alignment ofsaidfirst and second half image.

2. An arrangement as set forth in claim 1, further. comprising firstdiaphragm means positioned between said oscillating mirror means andsaid first and second photosensitive means, said first diaphragm meanshaving a first and second slit extending parallel to said predeterminedaxis said slit allowing transmittal of a selected portion of saidreflected first and second half image to said first and secondphotosensitive means, respectively.

3. An arrangement as set forth in claim 2, further comprising seconddiaphragm means arranged between said optical means and said oscillatingmirror means, said second diaphragm means having a first horizontalslit, and a second horizontal slit arranged below said first horizontalslit.

4. An arrangement as set forth in claim 3, wherein said oscillatingmirror means have an angle of oscillation smaller than the angle ofoscillation required for transmitting light along the full length ofsaidfirst and second horizontal strip onto said first and secondphotosensitive means.

5. An arrangement as set forth in claim 2, wherein said first diaphragmmeans have a first horizontal slit,

- and a second horizontal slit arranged below said first horizontalslit.

6. An arrangement as set forth in claim 1, wherein said moving meanscomprise servomotor means; further comprising switching circuit meansconnected to said AND-gate output for deenergizing said servomotor meansin response to substantially simultaneous receipt of said first andsecond scanning signals.

7. An arrangement as set forth in claim 6, further comprising first andsecond pulse-forming means respectivelyinterconnected between said firstphotosensitive means and said first AND-gate input, and said secondphotosensitive means and said second AND- gate input.

8, An arrangement as set forth in claim 7, wherein said first and secondpulse-forming means each comprise amplifier means, differentiatingmeans, and rectifier means.

9. An arrangement as set forth in claim 8, further comprising first andsecond Schmitt trigger means interconnected between said amplifier meansand said differentiation means of said first and second pulseformingmeans respectively.

10. An arrangement as set forth in claim 9, wherein said first andsecond pulse-forming means respectively comprise first and secondemitter-follower means connected between said rectifier means and saidfirst and second AND-gate input respectively.

11. An arrangement as set forth in claim 10, wherein the anode of saidthyristor means and an emittercollector circuit connected to saidservomotor.

13. An arrangement as set forth in claim 1, wherein said photosensitivemeans comprise photovoltaic cells.

1. In a photographic camera, an automatic focusing arrangement,comprising, in combination, lens means; moving means moving said lensmeans along a predetermined path between a first and second endposition; optical means creating a split image of a determined portionof an object to be photographed, said split image comprising a first andsecond half image displaced from each other along a first axis when saidlens means is incorrectly positioned for focusing said object andcoinciding when said lens means is correctly positioned for focusingsaid object; oscillating mirror means mounted to reflect said first andsecond half image, respectively, back and forth along a first and secondpredetermined path parallel to said predetermined axis; first and secondphotosensitive means respectively mounted in corresponding positionsalong said first and second predetermined path for receiving saidso-reflected first and second half images respectively and furnishing afirst and second scanning signal, respectively, in response thereto; andAND-gate means having a first and second input respectively connected tosaid first and second photosensitive means and an AND-gate outputconnected to said moving means, foR deenergizing said moving means inresponse to simultaneous receipt of said first and second scanningsignals, whereby said moving means are stopped upon alignment of saidfirst and second half image.
 2. An arrangement as set forth in claim 1,further comprising first diaphragm means positioned between saidoscillating mirror means and said first and second photosensitive means,said first diaphragm means having a first and second slit extendingparallel to said predetermined axis said slit allowing transmittal of aselected portion of said reflected first and second half image to saidfirst and second photosensitive means, respectively.
 3. An arrangementas set forth in claim 2, further comprising second diaphragm meansarranged between said optical means and said oscillating mirror means,said second diaphragm means having a first horizontal slit, and a secondhorizontal slit arranged below said first horizontal slit.
 4. Anarrangement as set forth in claim 3, wherein said oscillating mirrormeans have an angle of oscillation smaller than the angle of oscillationrequired for transmitting light along the full length of said first andsecond horizontal strip onto said first and second photosensitive means.5. An arrangement as set forth in claim 2, wherein said first diaphragmmeans have a first horizontal slit, and a second horizontal slitarranged below said first horizontal slit.
 6. An arrangement as setforth in claim 1, wherein said moving means comprise servomotor means;further comprising switching circuit means connected to said AND-gateoutput for deenergizing said servomotor means in response tosubstantially simultaneous receipt of said first and second scanningsignals.
 7. An arrangement as set forth in claim 6, further comprisingfirst and second pulse-forming means respectively interconnected betweensaid first photosensitive means and said first AND-gate input, and saidsecond photosensitive means and said second AND-gate input.
 8. Anarrangement as set forth in claim 7, wherein said first and secondpulse-forming means each comprise amplifier means, differentiatingmeans, and rectifier means.
 9. An arrangement as set forth in claim 8,further comprising first and second Schmitt trigger means interconnectedbetween said amplifier means and said differentiation means of saidfirst and second pulse-forming means respectively.
 10. An arrangement asset forth in claim 9, wherein said first and second pulse-forming meansrespectively comprise first and second emitter-follower means connectedbetween said rectifier means and said first and second AND-gate inputrespectively.
 11. An arrangement as set forth in claim 10, wherein saidfirst and second emitter-follower means comprise a first and secondtransistor respectively; and further comprising first and second biasingmeans respectively biasing said first and second transistor means tocut-off in the absence of said first and second scanning signalrespectively; and wherein said first and second scanning signalrespectively drive said first and second transistor to a conductivecondition.
 12. An arrangement as set forth in claim 11, wherein saidswitching circuit means comprise thyristor means having a gate connectedto said AND-gate output; and switching transistor means having a baseconnected to the anode of said thyristor means and an emitter-collectorcircuit connected to said servomotor.
 13. An arrangement as set forth inclaim 1, wherein said photosensitive means comprise photovoltaic cells.